mtPaint is a lightweight open source paint application for Linux and Windows. It is is aimed at creating indexed palette images and pixel art, and is designed to be simple and easy to use.

While the last stable mtPaint version was released back in 2011, there have been quite a few development releases since then, with the last one dating to June, 2016. I couldn't find a PPA with the latest mtPaint 3.50 development releases, so I created one to make it easy to install in Ubuntu and Linux Mint.

mtPaint features:

image manipulation:

quickly transform image gamma, brightness, contrast, saturation, hue, posterize from a single dialog, and preview the results in real time;

I also uploaded the latest mtPaint documentation to the PPA, as a separate package. To install it (it's listed as a "recommended" package and it will be automatically installed in Ubuntu in most cases, but not in Linux Mint), after adding the PPA, use the following command:

sudo apt install mtpaint-handbook

The documentation can be accessed from the mtPaint Help menu.

If you don't want to add the PPA, you can grab the deb from HERE (but you won't receive any updates!).

For other Linux distributions, download the latest mtPaint source code from GitHub.